Yes, the "LIMIT 1" is OK, thanks!
I didn't noticed the "not executed" in the explain output!
I have done some test comparing a plain table and a partitioned table performance in a particular statistical hypothesis (something explained here too:
http://tagschema.com ).
Mainly, data is produced and asked following an exponential distribution. So there a few very frequently accessed items and a lot of uncommon items.
Partitioning the two sets in different tables, the performance gain is interesting only after a few thousand rows.
http://www.slug.it/pgsqlpartSorry, the text is Italian, the code (sql schema and python test code) will be released in a few days (and you will need plpython from CVS if you are using 8.1), nevertheless pictures are already self explaining :-P
... I have seen a similar benchmark online but I cannot find it now to compare.
Sorry for my English, and open to comment about my simple benchmark,
Matteo Bertini
2006/8/16, Steve Atkins <steve@blighty.com>:
On Aug 16, 2006, at 8:23 AM, Matteo Bertini wrote:
> Hello all!
>
> I'm quite new to pg, but I'm using it quite a lot in the last few
> monts.
>
> Deeping in new features, I found a question: is it possible to hint
> an unique result from a select?
>
> Mainly, thinking about partitions, I'd like to create a small,
> frequently accessed partition and a big, rarely accessed partition.
>
> I'd like to hint pg to stop the query on the parent partition at
> the first found item (and so hint not to analyze all the childs),
> because I know the index I'm using is unique.
>
> Possible? Usefull?
>
"select foo from bar limit 1" ?
I don't know if there's any guaranteed ordering of results from
a union query, though, and that's what a query on a set of
inherited tables will expand to, pretty much.
Cheers,
Steve
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